The effects of several natural and synthetic steroids as inhibitors on the activity of .DELTA..sup.5 -3.beta.-hydroxysteroid dehydrogenase have been disclosed, including that of certain 2-cyano-.DELTA..sup.5 androstenes in Biochem. Biophys. Acta E 315, 233 (1973). The chemical procedures are known whereby 3-keto steroids can be converted to 2.alpha.-cyano-3-ketones via the [2,3-d]isoxazoles, and the substance "cyanoketone" has been described as a reference standard for enzyme inhibition, in J. Med. Chem. 6 1 (1963).